Well let's take a look...
Each time a unit is completely
destroyed within 7" of one or more units with this ability, except
in the Morale phase, pick one of those units to make a Soulburst
action. That unit can immediately do one of the following, even if it
has already done so in this turn:
If a transport is destroyed, any units embarked within it
immediately disembark (see below) before the transport model
is removed, but you must then roll one dice for each model you
just set up on the battlefield. For each roll of 1, a model that
disembarked (your choice) is slain.
Soulburst doesn't kick off until the model is completely destroyed. You place the models on the table and then remove the transport. I would assume, since the model is still on the battlefield, it's not completely destroyed, yet. But, the models don't get out until the transport is destroyed. But are destroyed and completely destroyed interchangable or different?
I think the models in the transport should be placed first before using soulburst simply because i see that as one step in the process of a transport being destroyed.